This invention relates to a solenoid apparatus and more particularly to a water cover arrangement for a solenoid apparatus particularly suitable for use as a solenoid switch of an engine starter.
An engine starter usually comprises a solenoid switch which operates a shift lever for shifting a drive unit including a pinion gear and a unidirectional clutch slidably mounted on an output rotary shaft toward a ring gear of an engine and which connects an electric source to a d.c. motor for driving the pinion gear. The basic structure and the function of the solenoid switch are well known in the art.
A vehicular engine starter is installed in an engine compartment of a vehicle, so that splashed water often enters into the engine starter through an opening formed around the pinion gear. This is particularly true in the case of the off-road vehicles. Therefore, in order to prevent ingress of water into the end portion of the plunger projecting outwardly from the end portion of the solenoid case of the solenoid switch, a flexible water cover or a flexible water-proof boot attached between the plunger and the end portion of the solenoid case is proposed in, for example, Japanes Utility Model Laid-Open No. 60-113940.
However, if space between the plunger and the solenoid case is completely covered or air-tightly sealed by the boot and when the solenoid plunger is moved out of and into the solenoid case, an undesirable pressure difference generates between the outside and the inside of the boot, causing an unexpected deformation of the flexible boot which may generate cracks in the boot. In order to prevent this, conventional water proof boot is provided at its flexible wall with a small vent hole which provides communication between both sides of the boot through the boot wall. The previously mentioned Japanese U.M. Laid-Open discloses the provision of a vent hole extending through the end portion of the plunger from one side of the boot to the other side of the boot to establish a communication therebetween.
However, since the vent holes of the above conventional arrangements are designed to be kept always open, water splash can enter into the interior of the boot through the vent hole under severe conditions. This is a particularly serious problem when the solenoid switch must be installed at a relatively lower level in the engine compartment due to the limited space in the engine compartment, for example.